Orbicularis oculi: orbital versus palpebral part
Orbicularis oculi, the round muscle around the eye, closes the eyelids: its palpebral (eyelid) part blinks gently and its orbital (eye socket) part squeezes tightly.
Remember
Tight eye closure is the orbital part and gentle blinking is the palpebral part, with the facial nerve supplying both. Opening the upper lid is a different muscle under a different nerve.
Orbicularis oculi is the round muscle that surrounds the eye, and it is responsible for closing the eyelids. Its parts do slightly different jobs.
The orbital part is the thicker ring of muscle around the bony eye socket (the orbit). It produces forceful eye closure, the tight squeeze used to screw the eyes shut. The palpebral part (palpebral means "of the eyelid") is thinner and paler, and lies within the lids themselves. It produces the gentle, automatic closure of a normal blink, which sweeps a thin layer of tears across the surface of the eye.
Both parts are muscles of facial expression, which are muscles that pull on the skin of the face rather than moving a joint. Both are supplied by the facial nerve (cranial nerve VII). The orbital part takes its supply from the temporal and zygomatic branches, the top two of the five branches into which the facial nerve divides inside the parotid gland, the large salivary gland in front of the ear. That is why surgery on the gland puts these branches at risk.
Opening the eye is the opposite action. Levator palpebrae superioris, the muscle that lifts the upper eyelid, is supplied by the oculomotor nerve (cranial nerve III), not by the facial nerve. A simple way to hold it: the facial nerve closes the eye and the oculomotor nerve opens it.
Key facts
- Orbital part
- a thick ring around the eye socket that produces forceful eye closure
- Palpebral part
- thin, pale muscle within the eyelids that gives the gentle, spontaneous blink
- Nerve supply
- both parts are supplied by the facial nerve, and the orbital part receives it through the temporal and zygomatic branches
- Opposite action
- levator palpebrae superioris raises the upper eyelid and is supplied by the oculomotor nerve
- Surgical risk
- facial nerve branches pass through the parotid gland, where they can be injured
- Word clue
- orbital means around the orbit and gives the tight squeeze, whereas palpebral means in the lids and gives the gentle blink
Exam traps
- The buccal branch of the facial nerve supplies muscles of the cheek and mouth, including the ring of muscle around the lips, but not the muscle around the eye. That muscle takes its supply from the temporal and zygomatic branches.
- The orbital part of orbicularis oculi is not supplied by the oculomotor nerve. Tight closure is the right job for that part, but its motor supply is the facial nerve, and the oculomotor nerve supplies the muscle that lifts the upper eyelid.
- Forceful closure of the eye is not the work of the palpebral part. It is produced by the orbital part, the thicker ring around the eye socket, whereas the palpebral part gives the gentler closure of ordinary blinking.
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